Plasma processing apparatus and focus ring

ABSTRACT

A plasma processing apparatus and a focus ring enables to perform uniform plasma processing over the entire surface of a substrate to be processed to thereby improve in-surface uniformity of plasma processing compared with conventional cases. The focus ring is disposed on a susceptor  2,  which serves to mount thereon a semiconductor wafer W and further functions as a lower electrode, to surround a periphery of the semiconductor wafer W. The focus ring  6  includes a ring member of a thin plate shape disposed to surround the periphery of the wafer W while maintaining a gap therebetween and a lower ring body installed below the semiconductor wafer and the ring member of the thin plate shape.

FIELD OF THE INVENTION

[0001] The present invention relates to a plasma processing apparatusand a focus ring employed therein for use in performing a predeterminedprocessing such as a plasma etching on a substrate to be processed,e.g., a semiconductor wafer.

BACKGROUND OF THE INVENTION

[0002] Plasma processing has been conventionally employed in themanufacture of a semiconductor device, an LCD (liquid crystal display),or the like to carry out a predetermined processing, e.g., filmformation, etching processing, or the like on a substrate to beprocessed, such as a semiconductor wafer or an LCD substrate, by using aplasma.

[0003] In case of a plasma etching process employing a parallel platetype etching apparatus, for example, a substrate to be processed ismounted on a mounting table (susceptor) installed in a plasma processingchamber, and a plasma etching is executed by allowing a plasma generatedwithin the plasma processing chamber to act on the substrate to beprocessed. Conventionally, a so-called focus ring is disposed tosurround the substrate to be processed in conducting such a plasmaetching process for the purpose of, e.g., enhancing an in-surfaceuniformity of the plasma etching process by ameliorating a discontinuityof the plasma at a peripheral portion of the substrate to therebyimprove an etching quality thereat (see, e.g., Japanese Patent Laid-openPublication No. 2002-246370, pages 2 to 5, FIGS. 1 to 6).

[0004] Referring to FIG. 8, there is illustrated a configuration of mainparts of the parallel plate type etching apparatus performing such aplasma etching process. In FIG. 8, a reference numeral 50 represents amounting table (susceptor) disposed in a plasma processing chamber (notshown).

[0005] The susceptor 50 further serves as a lower electrode and is of asubstantially disk shape made of a conductive material, e.g., having ananodic oxide film (alumite) formed at the surface thereof.

[0006] Provided on a wafer mounting surface of the susceptor 50 formounting thereon a semiconductor wafer W is an electrostatic chuck 51including an electrode 51 a embedded in an insulating film 51 b formedof an insulating material. Further, an annular focus ring 52 is disposedon the susceptor 50 to surround the semiconductor wafer W.

[0007] The susceptor 50 is formed of, e.g., aluminum as described above.Therefore, if there exists on the susceptor 50 a portion directlyexposed to plasma formed above the semiconductor wafer W, that portionmay be sputtered by the plasma, and as a result an undesirable sputteredfilm containing, e.g., aluminum, may be formed on the semiconductorwafer W.

[0008] For this reason, a diameter of the wafer mounting surface (wherethe electrostatic chuck 51 is formed) of the susceptor 50 is set to beslightly (for example, about 4 mm) smaller than that of thesemiconductor wafer W, as illustrated in FIG. 8. Further, by setting theinner diameter of a lower part of the focus ring 52 to be smaller thanthe diameter of the semiconductor wafer W, the lower part of the focusring 52 is extended to a space below a peripheral portion of thesemiconductor wafer W such that none of the top surface of the susceptor50 is directly exposed when viewed from the top.

[0009] The top surface of the focus ring 52 is set to be substantiallylevel with the top surface of the semiconductor wafer W. Therefore, atotal thickness of the focus ring 52 is far thicker than that (e.g.,about 0.8 mm) of the semiconductor wafer W.

[0010] As described above, in the conventional plasma processingapparatus, the focus ring is installed around the periphery of thesubstrate to be processed, to improve in-surface uniformity of plasmaetching. However, there is still a need to further enhance thein-surface uniformity of plasma etching, which has not been satisfiedwith the plasma processing apparatus using such a focus ring.

SUMMARY OF THE INVENTION

[0011] It is, therefore, an object of the present invention to provide aplasma processing apparatus capable of performing uniform plasmaprocessing over the entire surface of a substrate to be processed tothereby improve in-surface uniformity of plasma processing compared withconventional cases, and a focus ring employed therein.

[0012] In accordance with a first aspect of the present invention, thereis provided a plasma processing apparatus comprising:

[0013] a plasma processing chamber;

[0014] a susceptor installed within the plasma processing chamber formounting thereon a substrate to be processed;

[0015] a ring member disposed to surround a periphery of the substrateto be processed with a gap therebetween; and

[0016] a lower ring body placed below the substrate to be processed andthe ring member.

[0017] In accordance with a second aspect of the present invention,there is provided the plasma processing apparatus described in the firstaspect, wherein a ratio of an impedance per unit area of the ring memberto that of the substrate to be processed is equal to or less than about5.

[0018] In accordance with a third aspect of the present invention, thereis provided the plasma processing apparatus described in the secondaspect, wherein the ratio of the impedance per unit area of the ringmember to that of the substrate to be processed is equal to or less thanabout 3.

[0019] In accordance with a forth aspect of the present invention, thereis provided the plasma processing apparatus described in the thirdaspect, wherein the ratio of the impedance per unit area of the ringmember to that of the substrate to be processed is equal to or less thanabout 1.5.

[0020] In accordance with a fifth aspect of the present invention, thereis provided the plasma processing apparatus described in the firstaspect, wherein the ring member is made of a material having animpedance substantially identical to that of the substrate to beprocessed and a thickness of the ring member is equal to or less thanabout five times a thickness of the substrate to be processed.

[0021] In accordance with a sixth aspect of the present invention, thereis provided the plasma processing apparatus described in the firstaspect, wherein the ring member is made of the same material as thatforming the substrate to be processed and a thickness of the ring memberis equal to or less than about five times a thickness of the substrateto be processed.

[0022] In accordance with a seventh aspect of the present invention,there is provided the plasma processing apparatus described in the sixthaspect, wherein the substrate to be processed is a semiconductor wafermade of silicon and having a thickness of about 0.8 mm and the ringmember is made of silicon and has a thickness not greater than about 4mm.

[0023] In accordance with an eighth aspect of the present invention,there is provided the plasma processing apparatus described in the sixthaspect, wherein the substrate to be processed is a semiconductor wafermade of silicon and the ring member is made of silicon and has athickness substantially identical to that of the semiconductor wafer.

[0024] In accordance with a ninth aspect of the present invention, thereis provided the plasma processing apparatus described in the firstaspect, wherein the ring member is formed of SiC, aluminum having athermally sprayed coating formed on a surface thereof, quartz orceramics.

[0025] In accordance with a tenth aspect of the present invention, thereis provided the plasma processing apparatus described in the firstaspect, wherein the susceptor includes a conductive lower electrode andthe ring member is formed on a surface of the lower electrode by thermalspraying.

[0026] In accordance with an eleventh aspect of the present invention,there is provided the plasma processing apparatus described in the firstaspect, wherein the lower ring body serves to protect the susceptor froma plasma generated within the plasma processing chamber.

[0027] In accordance with a twelfth aspect of the present invention,there is provided a plasma processing apparatus comprising:

[0028] a plasma processing chamber;

[0029] a susceptor installed within the plasma processing chamber formounting thereon a substrate to be processed;

[0030] a ring member disposed to surround a periphery of the substrateto be processed with a gap therebetween; and

[0031] an electrostatic chuck formed on the susceptor to be locatedbelow the substrate to be processed and the ring member.

[0032] In accordance with a thirteenth aspect of the present invention,there is provided a plasma processing apparatus comprising:

[0033] a plasma processing chamber;

[0034] a susceptor installed within the plasma processing chamber formounting thereon a substrate to be processed; and

[0035] a ring member disposed to surround a periphery of the substrateto be processed with a gap therebetween,

[0036] wherein a ratio of an impedance per unit area of the ring memberto that of the substrate to be processed is equal to or less than about5.

[0037] In accordance with a fourteenth aspect of the present invention,there is provided a focus ring disposed on a susceptor to surround aperiphery of a substrate to be processed, the susceptor being installedwithin a plasma processing chamber of a plasma processing apparatus, thefocus ring comprising:

[0038] a ring member disposed to surround the periphery of the substrateto be processed with a gap therebetween; and

[0039] a lower ring body placed below the substrate to be processed andthe ring member.

[0040] In accordance with a fifteenth aspect of the present invention,there is provided the focus ring described in the fourteenth aspect,wherein a ratio of an impedance per unit area of the ring member to thatof the substrate to be processed is equal to or less than about 5.

[0041] In accordance with a sixteenth aspect of the present invention,there is provided the focus ring described in the fourteenth aspect,wherein the ring member is made of a material having an impedancesubstantially identical to that of the substrate to be processed and athickness of the ring member is equal to or less than about five times athickness of the substrate to be processed.

[0042] In accordance with a seventeenth aspect of the present invention,there is provided the focus ring described in the fourteenth aspect,wherein the ring member is made of the same material as that forming thesubstrate to be processed and a thickness of the ring member is equal toor less than about five times a thickness of the substrate to beprocessed.

[0043] In accordance with an eighteenth aspect of the present invention,there is provided the focus ring described in the fourteenth aspect,wherein the ring member is formed of SiC, aluminum having a thermallysprayed coating formed on a surface thereof, quartz, or ceramics.

[0044] In accordance with a nineteenth aspect of the present invention,there is provided the focus ring described in the fourteenth aspect,wherein the ring member is formed at a surface of a conductive lowerelectrode by thermal spraying.

[0045] In accordance with a twentieth aspect of the present invention,there is provided a focus ring disposed on a susceptor to surround aperiphery of a substrate to be processed, the susceptor being installedwithin a plasma processing chamber of a plasma processing apparatus, thefocus ring comprising:

[0046] a ring member disposed to surround the periphery of the substrateto be processed, wherein a ratio of an impedance per unit area of thering member to that of the substrate to be processed is equal to or lessthan about 5.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and other objects and features of the present inventionwill become apparent from the following description of preferredembodiments given in conjunction with the accompanying drawings, inwhich:

[0048]FIG. 1 illustrates a schematic configuration of a processingapparatus in accordance with a first preferred embodiment;

[0049]FIG. 2 describes a schematic configuration of main parts of theprocessing apparatus shown in FIG. 1;

[0050]FIG. 3 shows a variation of a uniformity of etching rate as afunction of a thickness of a focus ring;

[0051]FIG. 4 illustrates a relationship between an impedance ratio and auniformity of etching rate;

[0052]FIG. 5 describes an exemplary modified schematic configuration ofthe main parts of the processing apparatus of FIG. 1;

[0053]FIG. 6 shows another exemplary modified schematic configuration ofthe main parts of the processing apparatus of FIG. 1;

[0054]FIG. 7 explains a schematic configuration of main parts of aprocessing apparatus in accordance with a second preferred embodiment ofthe present invention; and

[0055]FIG. 8 illustrates a schematic configuration of main parts of aprior art plasma processing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] The present invention will now be described in detail withreference to the accompanying drawings.

[0057] Referring to FIG. 1, there is illustrated a schematicconfiguration of a plasma processing apparatus (plasma etchingapparatus) in accordance with a first preferred embodiment of thepresent invention. Reference numeral 1 represents a cylindricalprocessing chamber 1 forming a plasma processing room. The processingchamber 1 is made of, e.g., aluminum with an anodic oxide film (alumite)formed at the surface thereof, and the interior of the processingchamber 1 is configured to be hermetically sealed.

[0058] The processing chamber 1 is grounded and a susceptor (mountingtable) 2 serving as a lower electrode is provided in the processingchamber 1. The susceptor 2 is made of, e.g., aluminum having an anodicoxide film (alumite) formed at the surface thereof.

[0059] Installed on a wafer-mounting surface of the susceptor 2 is anelectrostatic chuck 3. As shown in FIG. 2, the electrostatic chuck 3includes an electrode 3 a embedded in an insulating film 3 b formed ofan insulating material, e.g., polyimide.

[0060] The susceptor 2 is supported in the processing chamber 1 in astate of vacuum via an insulating plate 4 such as ceramic, and theelectrode 3 a is connected to a DC power supply 5.

[0061] Further, an annular focus ring 6 is disposed on the susceptor 2to surround the periphery of the semiconductor wafer W. Theconfiguration of the focus ring 6 will be described later in detail.

[0062] Furthermore, formed within the susceptor 2 are a heat transfermedium path 7 for circulating an insulating fluid serving as a heattransfer medium for the control of the temperature of the susceptor 2and a gas channel 8 for supplying a temperature control gas, e.g., a Hegas, to the backside of the semiconductor wafer W.

[0063] By circulating the insulating fluid, which is regulated at apredetermined temperature, in the heat transfer medium path 7, thesusceptor 2 is maintained at a preset temperature. Further, by supplyingthe temperature control gas between the susceptor 2 and the backside ofthe wafer W through the gas channel 8, a heat transfer therebetween isfacilitated and, thus, the wafer W can be efficiently controlled to bemaintained at a predetermined temperature with a high precision.

[0064] Further, connected around the center of the susceptor 2 is afeeder line 10 for supplying a high frequency power, which in turn iscoupled via a matching unit 11 to a high frequency power supply (RFpower supply) 12 for supplying a high frequency power of a predeterminedfrequency.

[0065] Furthermore, formed outside the periphery of the focus ring 6 isan annular exhaust ring 13 provided with a plurality of exhaustapertures. A processing space within the processing chamber 1 isevacuated to a predetermined vacuum level through the exhaust ring 13by, e.g., a vacuum pump of a gas exhaust unit 15 coupled to a gasexhaust port 14.

[0066] Further, a grounded showerhead 16 is disposed above the susceptor2 on a ceiling portion of the processing chamber 1 to face the susceptor2 in parallel. Accordingly, the susceptor 2 and the showerhead 16 serveas a pair of electrodes (a lower electrode and an upper electrode,respectively).

[0067] The showerhead 16 is provided at a lower surface thereof with aplurality of gas injection openings 17 and has a gas inlet opening 18 atan upper portion thereof. Furthermore, formed within the showerhead 16is a gas diffusion cavity 19. Connected to the gas inlet opening 18 is agas supply line 20, which is led to a gas supplying system 21. The gassupplying system 21 includes a mass flow controller (MFC) 22 forcontrolling a gas flow rate and a process gas supply source 23 forsupplying a process gas, e.g., etching.

[0068] An annular magnetic field forming mechanism (ring magnet) 24 isdisposed around the processing chamber 1 to be concentric therewith, andserves to form a magnetic field in the processing space between thesusceptor 2 and the showerhead 16. The magnetic field forming mechanism24 is controlled to revolve about the processing chamber 1 by a rotationunit 25.

[0069] In the following, there will be provided a detailed descriptionof the configuration of the focus ring 6 mentioned above. As shown inFIG. 2, the focus ring 6 includes a ring member 6 a and a lower ringbody 6 b. The ring member 6 a is of a thin plate shape and is disposedto surround the periphery of the semiconductor wafer W, whilemaintaining a predetermined gap therefrom. The lower ring body 6 b ispositioned between and below the semiconductor wafer W and the ringmember 6 a, so that the susceptor 2 is prevented from being directlyexposed through the gap to a plasma in the processing space. The lowerring body 6 b is accomodated in a groove formed in the susceptor 2 andserves to protect a surface thereof. Further, the lower ring body 6 b isa consumable part consumed by a plasma and, thus, is replaceable.

[0070] Further, an impedance of the ring member 6 a per unit area (ahigh frequency impedance) is set to be not greater than about five timesthat of the semiconductor wafer W.

[0071] In accordance with the first embodiment, both the ring member 6 aand the lower ring body 6 b are made of silicon, which is the samematerial as used to form the semiconductor wafer W. In such a case, bysetting the thickness of the ring member 6 a to be equal to or less thanabout five times (about 4.0 mm) the thickness (about 0.8 mm) of thesemiconductor wafer W, the impedance per unit area of the ring member 6a can be adjusted to be not greater than about five times that of thesemiconductor wafer W. In the first embodiment, however, the thicknessof the ring member 6 a is set to be substantially identical to that ofthe semiconductor wafer W, as shown in FIG. 2.

[0072] Accordingly, the impedance per unit area of the ring member 6 ais also approximately identical to that of the semiconductor wafer W.

[0073] The reason for setting the impedance per unit area of the ringmember 6 a to be not greater than about five times that of the wafer Wis as follows.

[0074] The inventors of the present invention conducted a series ofexperiments and found that there occurs a difference between sheathvoltages formed above the wafer W and the focus ring 52, respectively,as indicated by a dotted line in FIG. 8, in case of employing theconventional focus ring 52 configured as shown in FIG. 8. Suchdiscontinuity of the sheath voltages was considered to be one of thefactors hampering a uniform processing of plasma etching at a peripheralportion of the wafer. Thus, it was expected that the uniformity of theetching processing would be improved by leveling the sheath voltages.

[0075] Further, the inventors viewed that the sheath voltages would beleveled by making the impedance per unit area of the focus ringapproximate to that of the semiconductor wafer W, to enhance theuniformity of the etching. Three focus rings having thicknesses of about8 mm, 4 mm, 2.4 mm, respectively, were fabricated by using silicon,which is the same material as that forming the semiconductor wafer W,and an etching processing was conducted for each case.

[0076]FIG. 3 shows a result of such etching processes, wherein thevertical axis represents a normalized etching rate (normalized by anetching rate measured at a position about 135 mm apart from the centerof the wafer), while the horizontal axis stands for a distance from thecenter of the wafer. As shown therein, it can be seen that a uniformityof the etching rate could be improved, especially at the peripheralportion of the wafer W, by employing a focus ring having a smallerthickness (thus, having an impedance per unit area closer to that of thesemiconductor wafer).

[0077]FIG. 4 also shows the experimental result with a vertical axisrepresenting a uniformity (±%) of an etching rate at the peripheralportion of the wafer W and a horizontal axis defining an impedance ratioper unit area (an impedance per unit area of the focus ring/an impedanceper unit area of the wafer W).

[0078] As shown in FIG. 4, by setting the impedance per unit area of thering member 6 a to be not greater than about five times that of thesemiconductor wafer W, the uniformity of the etching rate can becontrolled within ±5%, which is generally required in variousmanufacturing processes.

[0079] Furthermore, there may be required to maintain the uniformity ofthe etching rate within ±3% depending on manufacturing processes. Suchrequirement can be satisfied by setting the impedance per unit area ofthe ring member 6 a to be not more than about four times that of thesemiconductor wafer W.

[0080] Still further, the uniformity of the etching rate can be furtherenhanced by setting the impedance per unit area of the ring member 6 anot to be greater than about 3 times or 1.5 times that of thesemiconductor wafer W.

[0081] Though the first embodiment has been described for the case wherethe ring member 6 a is made of the same material as that forming thesemiconductor wafer W, i.e., silicon, it is also possible to form thering member 6 a by using another material such as SiC, aluminum with athermally sprayed coating (e.g., a thermally sprayed coating of Y₂O₃)formed on the surface thereof, quartz, ceramics, or the like. In such acase, the relationship between the impedance ratio and the thicknesswould be different from that described above since a dielectric constantand a conductivity of the ring member are different from those of thesemiconductor wafer W.

[0082] In fact, the semiconductor wafer W is formed of a silicon oxidefilm (SiO₂), a silicon nitride film (SiN), polysilicon, a metal film, alow-k film, and the like, in addition to the silicon substrate (Si).However, if the impedance of the semiconductor wafer W is predominantlydependent on an impedance of the silicon substrate (Si), the latter canbe regarded as the impedance of the semiconductor wafer W, withouthaving to consider an impedance of another material, e.g., the siliconoxide film (SiO₂).

[0083] Accordingly, a material (for example, silicon) having animpedance identical to that of the silicon substrate (Si) may beconsidered to have the same impedance as that of the semiconductor waferW (a substrate to be processed). Further, in case of employing amaterial such as SiC having a controllable impedance in lieu of thesilicon, it is possible to adjust the impedance of that material to besubstantially identical to that of the silicon substrate (Si).

[0084] Further, in case of forming a coating of, e.g., Al₂O₃ or Y₂O₃, onthe ring member 6 a, an impedance of that coating need not be consideredif its influence on the impedance per unit area of the whole ring member6 a is insignificant. However, the impedance of the coating may have asignificant influence on the total impedance of the ring member 6 a andthe coating depending on a material (a basic material) forming the ringmember 6 a and the thickness thereof and, further, depending on amaterial forming the coating and its thickness. In such a case, it isrequired to determine the materials for the ring member 6 a and thecoating and the thickness thereof by considering the impedance that thecoating might have.

[0085] As described above, the ring member 6 a is thinner than, e.g.,the conventional focus ring 52 illustrated in FIG. 8. In the firstembodiment, particularly, the thickness of the ring member 6 a is set tobe substantially identical to that of the semiconductor wafer W.Therefore, it is impossible to arrange a part of the ring member 6 a tobe disposed below the peripheral portion of the semiconductor wafer W.Thus, in the first embodiment, the focus ring 6 is designed to furtherinclude the lower ring body 6 b in addition to the ring member 6 a.

[0086] By disposing the lower ring body 6 b between and below thesemiconductor wafer W and the ring member 6 a, the susceptor 2 can beprotected.

[0087] Further, by forming a mounting surface for the ring member 6 a tobe higher than a mounting surface for the electrostatic chuck 3 andplacing a thermally sprayed coating 62 at a portion where the susceptor2 between the electrostatic chuck 3 and the ring member 6 a is exposedto the plasma, as shown in FIG. 5, the lower ring body 6 b is notrequired even in case the focus ring is of a shape similar to that ofthe conventional focus ring 52 illustrated in FIG. 8. In FIG. 5, thering member 6 a is made of silicon and its thickness is set to be abouttwice as large as that of the semiconductor wafer W. And the focus ringin FIG. 5 is formed of the ring member 6 a only, unlike the focus ring 6shown in FIGS. 1 and 2 having the ring member 6 a and the lower ringbody 6 b.

[0088] Further, as shown in FIG. 6, it may be preferable to set thediameter of the electrostatic chuck 3 installed at the mounting surfacefor the semiconductor wafer W to be virtually identical to that of thesusceptor 2 and locate the electrostatic chuck 3 under the semiconductorwafer W and the ring member 6 a. In such a case, the lower ring body 6 bis not needed, and the ring member 6 a is mounted on the electrostaticchuck 3 together with the semiconductor wafer W. By employing thisconfiguration, a simple structure can be obtained capable of protectingthe susceptor 2 from the plasma without recourse to the lower ring body6 b. Further, the focus ring provided in FIG. 6 is also formed of onlythe ring member 6 a unlike the focus rings illustrated in FIGS. 1 and 2having the ring member 6 a and the lower ring body 6 b.

[0089] Since the thickness of the ring member 6 a is configured to beapproximately identical to that of the semiconductor wafer W in thefirst embodiment, shown in FIGS. 2 and 6 as described above, a height ofthe mounting surface of the susceptor 2 for the ring member 6 a can bemade to be substantially identical to that of the mounting surface ofthe susceptor 2 for the semiconductor wafer W. Accordingly, lapping ofboth the mounting surface can be carried out simultaneously, therebyreducing a processing cost while improving a precision of theprocessing.

[0090] Further, a dotted line depicted in FIG. 2 represents a sheathvoltage formed above the semiconductor wafer W and the ring member 6 a.

[0091] In the following, there will be described a processing sequenceof a plasma etching processing employing the plasma etching apparatusconfigured as described above.

[0092] First, a gate valve (not shown) provided on the processingchamber 1 is opened; and a semiconductor wafer W is carried by atransfer device (not shown) into the processing chamber 1 from aneighboring load lock chamber (not shown) and is mounted on thesusceptor 2. Then, the transfer device is withdrawn from the processingchamber 1 and the gate valve is closed. A predetermined DC voltage issupplied from the DC power supply 5 to the electrode 3 a of theelectrostatic chuck 3, so that the wafer W is adsorbed to theelectrostatic chuck 3 to be maintained thereon.

[0093] Thereafter, the processing chamber 1 is evacuated to apredetermined vacuum level, e.g., 1.33 Pa to 133 Pa, by the vacuum pumpof the gas exhaust unit 15. At the same time, a predetermined etchinggas is supplied into the processing chamber 1 from the process gassupplying system 21.

[0094] Then, a predetermined frequency, e.g., a high frequency rangingfrom ten to two hundred MHz exclusive, is supplied from the highfrequency power supply 12 to the susceptor 2 via the matching unit 11.As a result, a plasma is generated in a space between the susceptor 2and the showerhead 16 to thereby perform an plasma etching of thesemiconductor wafer W.

[0095] In the first embodiment, a uniform sheath voltage is formed abovethe semiconductor wafer W and the focus ring 6, while etching thesemiconductor wafer w by the plasma. Accordingly, a uniform plasmaetching processing can be conducted on the entire surface of thesemiconductor W, thereby improving an in-surface uniformity of theplasma etching processing compared to conventional cases.

[0096] Furthermore, since the thickness of the ring member 6 a issmaller than that of the conventional one, a thermal capacity thereof isreduced, enhancing the response to a temperature change. Accordingly,though the plasma etching processing is conducted plural times, thetemperature of the focus ring is maintained at a same level, so that theinfluence of the temporal change in the temperature of the focus ring onthe plasma etching processing can be reduced.

[0097] Upon the completion of the predetermined etching of thesemiconductor wafer W, the high frequency power from the high frequencypower supply 12 is turned off to stop the plasma etching process andthen the semiconductor wafer W is unloaded from the processing chamber 1in a reverse order of the above-described sequence.

[0098] Hereinafter, a second preferred embodiment of the presentinvention will be described with reference to FIG. 7. In FIG. 7, areference numeral 76 a represents a thermally sprayed ring (a ring witha small thickness) formed by thermally spraying Si on a lower electrode(susceptor) 2 made of aluminum for example. A reference numeral 72indicates a thermally sprayed coating of Y₂O₃ for covering a portion ofthe lower electrode exposed to the plasma.

[0099] In the second embodiment, the thermally sprayed ring 76 a isemployed in lieu of the ring member 6 a of the thin plate shape used inthe first embodiment. Since the thermally sprayed ring 76 a is formed onthe electrode by the thermal spraying of Si, the thickness of thethermally sprayed ring 76 a can be readily controlled to besubstantially identical to that of the semiconductor wafer W.Accordingly, an impedance per unit area of the thermally sprayed ring 76a can be made to be substantially identical to that of the semiconductorwafer W.

[0100] The thermally sprayed ring 76 a can be formed by an atmosphericplasma spraying method, a plasma spraying method, a high velocity flamespraying method, a detonation gun process method, or the like. Though itis preferable that the thermally sprayed ring 76 a has a thicknessvirtually identical to that of the semiconductor wafer W, it is alsopossible to form the thickness of the thermally sprayed ring 76 a to besmaller than that of the semiconductor wafer W since it is formed bythermal spraying. Furthermore, the thickness of the thermally sprayedring 76 a can be made to be larger than that of the semiconductor waferW.

[0101] In addition, the material for the thermally sprayed ring 76 a isnot limited to Si. That is, the thermally sprayed ring 76 a can also beformed of, e.g., SiC, Y₂O₃, Al₂O₃, YF₃, or the like. The thermallysprayed coating 72 can also be formed of Si, Sic, Al₂O₃, YF₃, or thelike as in the case of the thermally sprayed ring 76 a.

[0102] Furthermore, a focus ring disclosed in the second embodiment isformed of only the thermally sprayed ring 76 having the small thickness.

[0103] Though the preferred embodiments have been described for the caseof applying the present invention to the plasma etching of thesemiconductor wafer W, the present invention is not limited thereto.That is, the present invention can also be applied to, e.g., a plasmaprocessing of an LCD substrate.

[0104] As described above, the present invention enables a uniformplasma processing over the entire surface of a substrate to beprocessed, thereby improving an in-surface uniformity of the plasmaprocessing compared with conventional cases.

[0105] While the invention has been shown and described with respect tothe preferred embodiments, it will be understood by those skilled in theart that various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A plasma processing apparatus comprising: aplasma processing chamber; a susceptor installed within the plasmaprocessing chamber for mounting thereon a substrate to be processed; aring member disposed to surround a periphery of the substrate to beprocessed with a gap therebetween; and a lower ring body placed belowthe substrate to be processed and the ring member.
 2. The apparatus ofclaim 1, wherein a ratio of an impedance per unit area of the ringmember to that of the substrate to be processed is equal to or less thanabout
 5. 3. The apparatus of claim 2, wherein the ratio of the impedanceper unit area of the ring member to that of the substrate to beprocessed is equal to or less than about
 3. 4. The apparatus of claim 3,wherein the ratio of the impedance per unit area of the ring member tothat of the substrate to be processed is equal to or less than about1.5.
 5. The apparatus of claim 1, wherein the ring member is made of amaterial having an impedance substantially identical to that of thesubstrate to be processed and a thickness of the ring member is equal toor less than about five times a thickness of the substrate to beprocessed.
 6. The apparatus of claim 1, wherein the ring member is madeof the same material as that forming the substrate to be processed and athickness of the ring member is equal to or less than about five times athickness of the substrate to be processed.
 7. The apparatus of claim 6,wherein the substrate to be processed is a semiconductor wafer made ofsilicon and having a thickness of about 0.8 mm and the ring member ismade of silicon and has a thickness not greater than about 4 mm.
 8. Theapparatus of claim 6, wherein the substrate to be processed is asemiconductor wafer made of silicon and the ring member is made ofsilicon and has a thickness substantially identical to that of thesemiconductor wafer.
 9. The apparatus of claim 1, wherein the ringmember is formed of SiC, aluminum having a thermally sprayed coatingformed on a surface thereof, quartz or ceramics.
 10. The apparatus ofclaim 1, wherein the susceptor includes a conductive lower electrode andthe ring member is formed on a surface of the lower electrode by thermalspraying.
 11. The apparatus of claim 1, wherein the lower ring bodyserves to protect the susceptor from a plasma generated within theplasma processing chamber.
 12. A plasma processing apparatus comprising:a plasma processing chamber; a susceptor installed within the plasmaprocessing chamber for mounting thereon a substrate to be processed; aring member disposed to surround a periphery of the substrate to beprocessed with a gap therebetween; and an electrostatic chuck formed onthe susceptor to be located below the substrate to be processed and thering member.
 13. A plasma processing apparatus comprising: a plasmaprocessing chamber; a susceptor installed within the plasma processingchamber for mounting thereon a substrate to be processed; and a ringmember disposed to surround a periphery of the substrate to be processedwith a gap therebetween, wherein a ratio of an impedance per unit areaof the ring member to that of the substrate to be processed is equal toor less than about
 5. 14. A focus ring disposed on a susceptor tosurround a periphery of a substrate to be processed, the susceptor beinginstalled within a plasma processing chamber of a plasma processingapparatus, the focus ring comprising: a ring member disposed to surroundthe periphery of the substrate to be processed with a gap therebetween;and a lower ring body placed below the substrate to be processed and thering member.
 15. The focus ring of claim 14, wherein a ratio of animpedance per unit area of the ring member to that of the substrate tobe processed is equal to or less than about
 5. 16. The focus ring ofclaim 14, wherein the ring member is made of a material having animpedance substantially identical to that of the substrate to beprocessed and a thickness of the ring member is equal to or less thanabout five times a thickness of the substrate to be processed.
 17. Thefocus ring of claim 14, wherein the ring member is made of the samematerial as that forming the substrate to be processed and a thicknessof the ring member is equal to or less than about five times a thicknessof the substrate to be processed.
 18. The focus ring of claim 14,wherein the ring member is formed of SiC, aluminum having a thermallysprayed coating formed on a surface thereof, quartz, or ceramics. 19.The focus ring of claim 14, wherein the ring member is formed at asurface of a conductive lower electrode by thermal spraying.
 20. A focusring disposed on a susceptor to surround a periphery of a substrate tobe processed, the susceptor being installed within a plasma processingchamber of a plasma processing apparatus, the focus ring comprising: aring member disposed to surround the periphery of the substrate to beprocessed, wherein a ratio of an impedance per unit area of the ringmember to that of the substrate to be processed is equal to or less thanabout 5.